Means for varying the timing of valve actuation of internal combustion engines are well known. Such means typically take the form of a camshaft phaser or an element of a valve train, such as rocker arms, roller finger followers, hydraulic valve lifters, or hydraulic lash adjusters, provided with a mechanism for switching between a valve activating mode and a valve deactivating mode. VVA/VVT is especially well known in spark-ignited (SI) engines, in which it is an essential element of various schemes for improving fuel economy. However, camshaft phasers, while readily applied to SI engines, are not as suitable for CI engines since cam phasing introduces the risk of catastrophic valve-to-piston collisions due to the close proximity of the piston crown to the cylinder head at top dead center (TDC) at which point the valves are obliged to be closed. For this reason, an alternative technology, known in the art as “lost motion”, has found increasing favor for VVT/VVA in CI engines, since much of the functionality of existing SI VVT/VVA systems is available without danger of piston/valve collisions.
The potential importance of VVT/VVA to CI engine performance is coming to be realized within the engine industry. The firing of an SI engine is readily and accurately controlled by simply controlling the timing of the ignition spark. The firing of a CI engine, and more particularly so the firing of a controlled auto-ignition (CAI) or homogeneous charge compression ignition (HCCI) engine on the other hand, is governed by a plurality of independent or loosely-dependent variables which conspire to cause the fuel/air charge to explode at some resultant combination of temperature, pressure, and mixture.
These variables, which include, but may not be limited to, cylinder temperature, cylinder pressure, valve train timing and wear, fuel injection timing and accuracy, homogeneity of the fuel/air charge, and thermal load of the fuel/air charge, can vary from cylinder to cylinder in an individual engine and furthermore can vary for any given cylinder from one firing cycle to the next. Thus, in the prior art the exact point in the compression stroke at which the compressed charge in a cylinder will ignite cannot easily be predicted or controlled to a very high degree of certainty, and in practice the cylinders of a multiple-cylinder HCCI engine may not fire with a degree of uniformity required to meet future performance standards.
In a CI engine, the trapped air mass is the “charge volume” in the cylinder upon which compression work is done. Because adiabatic compression of the charge volume is the mechanism by which CI ignition is induced, an important ignition factor is the “Effective Compression Ratio” (ECR) within the cylinder. Thus, direct control of ECR can provide improved control of firing timing both in individual cylinders and among the cylinders in a CI engine. Controlling ECR by increasing the compression ratio can improve cold start characteristics, and by decreasing the compression ratio can improve engine performance. Other engine control strategies that can be attained by strategically controlling the opening, closing and lift of the gas valves in a CI engine, as more fully described in co-pending U.S. patent application Ser. No. 11/027,109, include in-cylinder swirl of intake gases to provide effective mixing of injected fuel and air, and controlled Exhaust Gas Recirculation (EGR) to control combustion initiation and burn rates, while lowering flame temperatures for reduced NOx emissions.
In a Type 2 engine valve train, a roller finger follower (RFF) typically is interposed between an inwardly-opening poppet valve stem tip at one end and a hydraulic lash adjuster (HLA) at the distal end, with a cam lobe providing motivation to the RFF at an intermediate point. For reasons of good dynamic performance at high speed, low friction, and convenient packaging, this mechanism is rapidly becoming the valve train of choice for many new light-duty engines today, both SI and CI.
In a Type 3, 4, or 5 valve train, a rocker arm pivots on a rocker shaft, with one end of the rocker arm being motivated by the camshaft either directly or through the medium of a follower and/or pushrod, and the other end actuating the engine valve. For reasons of valve train cost, packaging convenience, or tradition, these systems are frequently used for medium- to heavy-duty engines and may or may not use an HLA. (For simplicity of presentation hereinbelow, Type 3 should be understood to mean all central-pivot rocker arm engines, including Types 4 and 5.)
In another version of the Type 3 valve train, the rocker arm pivots on an inverted HLA instead of a rocker shaft. Since the HLA is stationary, this type of valve train offers reduced dynamic mass advantages over other Type 3 valve train.
Lost motion means in a valve train element switches the linear motion imparted to the valve train by a rotating cam between either of a valve stem/lifter/pushrod or rocker arm and a lost motion spring/piston/accumulator. In the valve activating mode, the switchable element is mechanically and hydraulically competent to transfer the motion instructions of the cam to the valve; but in the valve deactivating mode, the switchable element collapses by a controlled amount and at the appropriate time in some fashion to “lose” the motion of the cam and belay those instructions to the valve. See, for example, U.S. Pat. No. 6,883,492.
Serious drawbacks of such known VVA/VVT systems are that they employ engine lubricating oil as the hydraulic medium, which tends to be dirty, carbon-laden and relatively high viscosity, requiring relatively large passageways to prevent flow failure; they employ a relatively bulky, powerful solenoid control valve which because of its size has a relatively slow speed of response; and they introduce significant additional complexity to the cylinder head that, in so doing, creates problematic packaging and manufacturing issues.
It is highly desirable that any apparatus and control system for improved control of ECR be applicable to existing arrangements of Type 2 and Type 3 engine valve trains with a minimum of engine redesign.
What is needed in the art is an improved means for controlling engine strategies such as, for example, ECR, EGR and in-cylinder swirl in a CI engine.
What is further needed is that such improved means be applicable to, and controllable for, individual cylinders in a multiple cylinder engine.
It is a principal object of the present invention to improve control of various engine control strategies in a CI engine.
It is a further object of the invention to provide such improved control with minimum redesign requirements for Type 2 and Type 3 engines.
It is a still further object of the invention to provide such improved control through novel adaptation of existing fuel injection equipment (FIE) technologies which have been demonstrated to have the speed of response, precision, and durability required for an ECR control system.